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United States Patent Ofice 3,385,073 Patented May 28, 1968 3,385,073 REFRIGERATION SYSTEM FOR SHIPPING PERISHABLE COMMODITIES Charles D. Snelling, Allentown, Pa., assignor to Cryo- Therm, Inc, Fogelsville, Pa., a corporation of Delaware Filed Get. 6, 1966, Ser. No. 584,858 Claims. (Cl. 62-45) ABSTRACT OF THE DISCLOSURE A refrigeration system for shipping perishable commodities in transport compartments is disclosed comprising heat exchange means, means for maintaining the heat exchange means at a refrigerating temperature, a heat transfer circulating system coupled to the exchange means for controlling the temperature of perishable commodities, and a heat transfer fluid in the circulating system in amounts such that the major portion of the heat transfer circulating system is substantially flooded with the heat transfer fluid.

This invention relates to a refrigerating system for use in shipping perishable commodities in transport compartments and, in particular, to a system and method for maintaining and controlling the desired refrigerating temperature of perishable commodities during transport in containerized packages, in trucks, railway cars, boats or other means of vehicular food conveyance. This invention also relates to means and methods for controlling the atmosphere of the compartment containing the com modity. The term transport compartment used herein is meant to include the foregoing method and means for shipping perishable commodities.

The need to transport fresh foods, such as lettuce, strawberries, tomatoes and the like, or frozen foods for long distances in an insulated containerized package or transport compartment, such as by motor trucks, boats or railway car under refrigerated conditions is well known. Heretofore, this had generally been accomplished by packing and periodically re-packing a portion of the vehicle or trailer with ice, or by using various mechanical refrigeration systems, such as a gasoline powered refrigerant compressor system.

While the foregoing systems have in the broad sense achieved their aims, they have not been entirely satisfactory. Packing and re-packing with ice is inconvenient and expensive. Both ice and mechanic refrigeration systems did not always provide the desired temperature control, the temperatures being usually warmer than desirable. Mechanical systems require constant attention and may be subject to break down enroute to the shipping destination. Moreover, in neither of these systems were provisions made to control the atmosphere in the refrigerating space.

Attempts to overcome these problems have led to the use of systems involving cryogenic materials, eg liquid nitrogen, as a cooling source. Such systems which generally do not require a combination of moving components or parts for operation as in mechanical refrigeration systems, use a cryogenic vessel in which the liquid cryogenic material is kept. In the case of liquid nitrogen, this material is sprayed or distributed among the contents of the trailer under thermostatically controlled conditions, the nitrogen being fed through tubes located on the roof of the trailer. These attempts represent a marked improvement for refrigerated transport. For one thing, the liquid nitrogen is safe and reliable and, as started above, requires no moving components for its effective use as a coolant. In addition, liquid nitrogen has a high cooling capacity due to its latent heat of vaporization and the specific heat of the ultra-cold liquid (minus 320 F.) and, therefore, a

little goes a long way. Thus, systems using liquid nitrogen may be light and hav long holding power. However, a drawback is that feeding of nitrogen as a liquid or gas into the contents of a truck may frequently result in freezing and re-freezing of delicate contents, with resulting damage and loss.

In addition, nitrogen gas in too high a proportion and an insufficiency of oxygen has a deleterious effect on many kinds of fresh produce. Moreover, since the distribution of cold (i.e. low temperature) in such system is 'by gas circulation, which is not always sufiicient when a truck is fully loaded, the contents at the bottom of the vehicle may tend to be warmer than the portion of the contents close to the nitrogen spray device.

I now provide a system which obviates the foregoing dis-advantages by utilizing a novel apparatus and method that do not require contacting the perishable commodity with cold nitrogen to control its temperature. However, I may bleed gaseous nitrogen, if it is desired, into the space where it is desired to maintain control of the atmosphere together with oxygen and carbon dioxide, but the primary heat exchange is achieved without contacting the food with nitrogen. In addition, I find that with my system, I can use any vaporizable cryogenic material to effect cooling.

It is thus the object of my invention to provide a system and method for effectively refrigerating perishable commodities.

Another object is to provide a refrigeration system and method in which a cryogenic material, such as liquid nitrogen, can be employed without requiring contacting the perishable substance with nitrogen.

A still further object is to provide a refrigeration system for containerized packages and/ or transport vehicles, such as trucks, in which the atmosphere surrounding the perishable substance as well as the temperature can be controlled.

These and other objects will more clearly appear from the following disclosure, the appended claims and the accompanying drawings, wherein:

FIG. 1 depicts the use of one embodiment of the invention as applied to a shipping container for food, be it a containerized package, a truck body or a compartment of a refrigerated railway car or boat;

FIG. 2 is a schematic illustrating one embodiment of the refrigeration system for carrying out the invention;

FIG. 3 is a simple circuit diagram showing one embodiment of a control circuit for thermostatically controlling a solenoid operated valve employed in controlling the feed of liquid nitrogen to a heat exchanger, not shown;

FIGS. 4 and 5 are illustrative of an embodiment of the invention as applied to a trailer truck;

FIG. 6 depicts another embodiment for obtaining re frigeration using solid carbon dioxide, that is Dry Ice, as the cryogenic material;

FIG. 7 is a cross section of a flat tube sheet of metal taken along lines '7-7 of FIG. 2;

FIG. 8 shows another embodiment of a refrigerating system in which an anti-freeze liquid may be used as a heat transfer fluid;

FIGS. 9 to 11 are illustrative of systems which may be employed to control the atmosphere within the chamber in which food is confined for shipment;

FIG. 12 depicts one embodiment of a heat exchanger which may be employed for precooling air before it is circulated into the food chamber; and

FIG. 13 is a block diagram of an embodiment that may be employed in controlling the atmosphere.

In its broad aspects, I provide as my invention a refrigenation system for shipping perishable commodities comprising, means for confining a vaporizable substance, exchange means cooperably associated with said confining means whereby the effect heat transfer between the contents of said confining means and said heat exchange means, a heat transfer circulating system positioned in association with the perishable commodities to be protected, means coupling the heat exchange means in circulation relationship with the heat transfer circulating system, and a heat transfer fluid in the heat transfer circulating system, the amount of said fluid and the relative position of the heat exchange means to the circulating system being such that the major portion of the heat transfer circulating system is substantially flooded with said heat transfer fluid.

In one embodiment of my invention, I may use a cryogenic vessel filled with liquid nitrogen as my cooling source (for example 100 liters) maintained at a selfgenerated pressure of 25 pounds per square inch via a relief valve. The cryogenic vessel is coupled by means of a liquid removal line and a controllable valve to a heatexchanger which is preferably located in the highest part of the truck or rail car for example, the roof. The inside surfaces of the truck chamber, for example, the roof, the floor, the side walls and possibly the end walls are preferably lined with interconnecting heat exchanger metal panels having an integrated array of circulating pathways or tubing which make up the circulating system. Such panels may be made from what is referred to in the trade as flat tube sheets or roll bonded sheets of aluminum, copper, steels or other metals. An example of a flat tube sheet is shown in FIG. 7. These tube panels are con nected in circulating relationship to themselves and from top and bottom to the heat exchanger, a gas return line being coupled from the top to the heat exchanger and a liquid feed line being connected from the heat exchanger to the bottom panel on the floor of the truck chamber.

The tubular pathways in the tube sheets are filled with a thermodynamic heat transfer fluid. Preferably, the circulating system is evacuated and a thermodynamic fluid such as Freon, alcohol, acetone, carbon tetrachloride, or the like, hermetically sealed therein. The amount of fluid added is sufiicient so that the tube panels are flooded or nearly flooded, while the heat exchanger is filled with gas, as a result of evaporation of the fluid, since it is sealed in the evacuated system. Thus, any heat transfer liquid which forms in the heat exchanger by condensation cooling flows by gravity to the tube panels, while any gas which forms due to heat absorption in the tube panels will rise and flow into the heat exchanger.

As illustrative of the foregoing, reference is made to FIG. 1 which shows an insulated transport compartment or container for confining perishable commodities, such as food. The compartment there disclosed may be a containerized package or box or part of a truck body or refrigerated railway car or boat. The construction shown is not to be construed as being the ultimate design to be employed, it being understood that many variations may be employed to carry out the invention. Thus, a cryogenic bottle 11 of nitrogen is shown in the forward part of chamber 12 for purposes of clarity in describing the embodiment, whereas it would preferably be hidden in a wall compartment to provide unencumbered spaces for stocking perishable foods and the like.

Thus, referring again to FIG. 1, chamber 12 is shown having bottom, top and side walls of tube panels 13, 14, 15 and 16, respectively, interconnected in circulating relationship with each at various points 17, 18, 19, etc., the tube panels having circulating therein a heat transfer fluid. The panels, which are preferably made of roll bonded aluminum or copper, or aluminum-base or copper-base alloys, line the inside walls of the chamber, which walls are insulated to prevent as much as possible the ingress of heat from the outside. The outside surface of the container may have a steel sheath 21 having adjacent to it a thick layer of foam plastic 22, e.g. urethane foam, or other suitable insulation, such as rock wool, reinforced fiber glass, asbestos, or the like, against which tube panels 13 to 16 are supported. Embedded in the roof insulation is a heat exchanger 23.

Cryogenic vessel 11 which contains liquid nitrogen 24 is coupled via tube 25 and a solenoid operable valve 35 to heat exchanger 23, the heat exchanger having a sinuous array of coils of heat exchanger tubes 26 with which tube 25 communicates. The cryogenic vessel has a relief valve 27 communicating with the gas above the liquid therein preset to maintain the liquid nitrogen-vapor under 25 pounds per square inch. Tube 25 communicates with tube 25a in the vessel, through which tube the nitrogen is forced by virtue of the pressure above the liquid in the vessel. Thus, nitrogen flowing through tube 25 and heat exchanger tubes 26 absorbs heat from the heat exchanger and then flows out as a gas through outlet 28 into the atmosphere. However, the waste nitrogen need not be disposed of as stated above, but may be used for atmosphere makeup for use inside the container to be described later.

Heat exchanger 23 is coupled to the tube panels via liquid feed line 29 from point 30 at the bottom of the heat exchanger to 31 at the lower portion or bottom of the set of tube panels. The tube panels are further coupled via vapor return line 32 from the top thereof to the top of heat exchanger 23 at 33, this being more clearly apparent from FIG. 2 which shows schematically cryogenic vessel 11a coupled via tube 251) and solenoid operable valve 35a to heat exchanger 23a, tube 251; communicating with heat exchanger tube 26a and the flowing out to the atmosphere at 280. As will be noted, heat exchanger 23a is coupled via liquid feed line 29a (heat transfer liquid) to the bottom of tube panel 16a at 31a, the tube panel in turn being coupled via gas return line 32a to the top of the heat exchanger at 3311.

As will be further noted, the tube panel 16a is substantially flooded with heat transfer fluid as shown at 36, the upper or top portion of the tube panel providing space in which heat transfer vapor is collected and returned to the top side of the heat exchanger at 33a. This constitutes the invention in its broad aspects except for a preferred embodiment which uses thermostats to control the extent and degree of refrigeration desired.

Referring to FIG. 3, a simple circuit is depicted show ing a source of power, e.g. a battery 38, coupled via lines 39 and 40 to a series arrangement of solenoid operable valve 35a of the cryogenic vessel as in FIG. 2, a thermostat T which is located strategically among the perishable contents of the container and limit thermostat T; which is located at the liquid line of the heat transfer fluid, the purpose of thermostat T being to prevent the heat transfer fluid from congealing should by happenstance an overcooling effect arise in the heat exchanger. For safety sake, this thermostat is set at a temperature of about 25 warmer than the freezing point of the thermodynamic heat transfer fluid used in the system. Thermostat T is capable of being set, let us say, at a temperature within the range of 0 to F., depending upon whether frozen or fresh foodstuffs are being shipped.

FIGS. 4 and 5 are illustrative of the use of the broad aspects of the invention as applied to shipment of perishables by truck. In FIG. 4 a truck body 41 is shown supported by Wheeled undercarriage 42 as shown, the body being depicted as having an outer sheath of metal 43 or other suitable structural material, a wall of insulation 44, e.g. urethane foam, substantially completely surrounding a food-carrying chamber 46 faced with interconnecting tube panels 47 to 50. Of course, the compartment 41 may be a containerized package or box carried by an open trailer. The panels may preferably communicate with each other via manifolds 47a to 500, said arrangement being also shown in FIG. 5. While these and the foregoing embodiments are shown with tube panels, it will be appreciated that ordinary tubing may be employed in their place as will be obvious to those skilled in the art.

In FIG. 5, insulated transport compartment in the form of a truck body is shown in side elevation looking at tube panel 48 comprising three sections 48b, 48c, and 48d connected to manifolds 47a. and 48a running the length of the trailer. Embedded in the insulated roof of the trailer is heat exchanger 51 having heat exchanger tubing 52 which communicates with nitrogen line 53 coupled to cryogenic vessel 54 having a pressure relief valve 55 set at 25 lbs./in. As will be noted, a solenoid operable valve 56 is provided and thermostats T and T T being strategically positioned according to the contents of the trailer, while T is positioned at the exit side of the liquid heat transfer fluid line 57 at 58. Liquid line 57 is coupled to the bottom of the tube panel at 59 where it enters manifold 48a. Gas return line 60 is shown coupled from the top of tube panel 48 of manifold 47a at 61 to the top of heat exchange 51 at 62.

Describing the broad aspects of the invention as illustrated by FIGS. 1 to 5, and, in particular, FIG. 5, thermostat T located strategically in the truck or on a side wall thereof will sense when the contents of the truck reach a temperature, let us say, one degree warmer than it is desired. At this point, the solenoid operable valve 56 (FIG. 5) in liquid nitrogen line 53 will allow liquid nitrogen under 25 lbs/in. pressure to flow from the cryogenic vessel into heat exchanger 51 where the nitrogen will vaporize due to the absorption of heat and flow out of exit tube 63 into the atmosphere. Solenoid operable valve 56 is activated by battery 38 or other suitable means of power.

As the surfaces in heat exchanger 51 of FIG. 5 are cooled by the liquid nitrogen, the heat transfer vapor sursoundin-g heat exchanger tubing 52 is condensed to a liquid and flows via line 57 to the bottom of tube panel 48b via manifold 48a. As condensation occurs, the pressure in the entire system is lowered and, thus, the relatively warmer thermodynamic liquid in various portions of the tube panels will boil or vaporize in just sufiicient quantities to remove the necessary heat. The vaporized liquid will rise up the tube panels and flow into the heat exchanger via line 60 where it is recondensed and so on. It will be appreciated that the thermodynamic liquid in the tubes will supply variable amounts of cooling at a given location depending upon how much heat is present, thus avoiding local overheating. When suflicient cooling has been achieved in the container of perishables, thermostat T strategically located relative to the contents will sense this and deactivate solenoid operable valve 56 to thereby slow down the cooling action. However, irrespective of the temperature at thermostat T the solenoid may be deactivated if the cooling effect is so great at the heat exchanger that the heat transfer fluid is in danger of being congealed or frozen at a temperature sensed by thermostat T When this occurs, the system will idle for a period until the congealed heat transfer fluid liquifies and its temperature drops to a temperature at which thermostat T is inoperable.

To minimize the possibilities of the heat transfer fluid from congealing, the heat exchanger can be properly designed so that the proper ratios of heat exchanger surfaces are employed and, if desired, by using concurrent flow techniques as contrasted with counter-flow methods of heat absorption. In the alternative, it may be desirable to limit the liquid nitrogen flow by use of either a temperature or pressure sensing device in the line of the heat transfer fluid so as to limit the temperature at which the fluid leaves the heat exchanger or the pressure to which the heat transfer gas is condensed in the heat exchanger. As will be evident, conventional sensing devices can be used in various ways in my system to achieve the foreple, urethane foam may be employed which is a good deal cheaper and lighter. It is not important that such a vessel may have a higher heat leak rate since it would in any event be located within the container of the perishables. In addition, the vessel would be provided with a relief valve to avoid undue pressure build-up within it should the temperature of the liquid nitrogen rise during transport.

As another embodiment of my invention, I may employ a system in which Dry Ice is used as the cryogenic material. In this instance, the heat exchanger would be constructed in the form of a box 65 as shown in FIG. 6 containing cubes or crushed lumps of Dry Ice 66. The box may be constructed with an outside sheath of metal 67 or other suitable construction material having supported thereagains-t a thick wall of insulation 68 of urethane foam or other suitable insulating material, the box having a cover 69 and side and bottom walls 70 to 72. Located against the inside walls are tube panels 73-, 74 and 75 interconnected by manifolds 76, 77, 78, 79 and 80, manifold 8t) surrounding the inner periphery of the box. Line 81, which represents the heat transfer vapor line enters at the top of the tube panel at manifold 76 and upon being condensed leaves the heat exchanger via liquid line 82. through solenoid operable valve 83. This valve would be controlled similarly as valve 35a in FIG. 3. A vent may be provided in box 65 to vent off gaseous carbon dioxide as it forms. This embodiment of my invention enables the use of comparatively inexpensive and readily available Dry Ice, instead of the less easily available and more frequently expensive liquid nitrogen.

FIG. 7 shows in cross section a tube panel as taken alone line 7-7 of FIG. 2. Two metal sheets or plates of, for example, aluminum, copper, steel, or the like, are bonded at their common interface 87 except for non-bondable areas which define passageways 88 when these areas are inflated after the sheets are bonded together at their bondable areas. While, as stated above, tube panels or flat tube sheets might be preferred as heat exchangers, other forms well known in the art may be employed.

In the embodiment of FIG. 8, I show schematically another system that may be employed that utilizes only the circulation of a cold fluid, such as alcohol, alcohol and water, anti-freeze mixtures of ethylene glycol and Water, to produce the desired refrigerating effect. There the heat exchanger in effect takes the form of a cyclone $0 which has a dual purpose. It enables heat exchange to take place by actual contact between cold nitrogen and the heat transfer fluid and also provides the means to effect the separation of warm nitrogen gas from the chilled fluid, it being appreciated that the term warm is used in a relative sense. The cyclone 90 communicates with the top of a tube panel 91, having a continuous pathway 92 therethrough which emanates at the bottom 93 and enters line 94 having a pump ,5 coupled across the line for pumping the heat transfer fluid (for example, an antifreeze mixture of ethylene glycol and water) to a point where liquid nitrogen is fed into the cyclone, the flow of liquid nitrogen serving also to aspirate the liquid refrigerant. Thus, the liquid refrigerant is pumped to nozzle 96 in which is coaxially supported nitrogen nozle 97, said nitrogen nozzle communicating with nitrogen line 8 coupled to cryogenic vessel 99 having a relief valve 100 pre-set for a given pressure release. As in the previous embodiments, a solenoid operable valve 101 may be provided in the nitrogen line controlled by a thermostat wiihin the food container as described similarly for FIG. 3. The thermostat may be connected in the circuit to shut off both the valve and the pump, or if desired, just the valve, since it may be desirable to keep the pump running even when the valve is off in order to maintain uniform coolness throughout the container until such time that the temperature at the thermostat rises and requires opening of the nitrogen valve.

As will be noted from FIG. 8, the cyclone has a tube outlet 102 coaxiaily supported therein, the cyclone being closed at 103, except for the opening in the tube. Thus, as the nitrogen and anti-freeze swirl around tube 102 and heat interchange takes place in the mixture, the warmer nitrogen gas leaves the system through said exit tube. The nitrogen gas may be vented into the atmosphere or Within the truck, depending on what seems desirable.

The foregoing cyclone system of heat exchange has several advantages. A hermetically sealed system is not required and the cyclone in effect does the job of a heat exchanger, while separating the gas from the chilled fluid, whereby efficient heat transfer results. Moreover, the cyclone is small, compact and cheap.

In systems employing nitrogen gas as the major portion of atmosphere as well as the coolant, it has been found that such systems were not always beneficial to many kinds of fresh produce. This generally was due to an insufliciency of oxygen. A controlled atmosphere during transport may be preferred where a low ripening rate is desired. A desirable atmosphere for the purpose may comprise 2 to 7% oxygen, 0.1 to 6% carbon dioxide and to 97.9% nitrogen. The carbon dioxide is generally naturally present as a ripening lay-product of the perishable commodity. A typical atmosphere may comprise 3% oxygen, 5% carbon dioxide and 92% nitrogen. In some instances, it may be desirable to add carbon dioxide from a tank carried for that purpose.

With my system, I can bleed back waste nitrogen together with outside air to make up the desired atmosphere and rely on the CO naturally produced by the perishable commodity. One embodiment of such a sys tem is shown in FIG. 9 which depicts a nitrogen gas line leaving a heat exchanger (not shown) of the type for example in FIG. 2, said nitrogen gas line entering venturi 109 to which venturi is coupled an air line 107 from outside the container or trailer having a valve 108 pre-set to provide an amount of air proportioned to the flow of nitrogen gas. The venturi aspirates the outside air by virtue of the fiow through of nitrogen and hence a pump is not required. Where there is no nitrogen flow through, no air will flow. The resulting mixed gases are then directed into the truck, outlet valve 110 being provided in exit line 111 to control the amount of circulation of the atmosphere. Valves 108 and 110 may be controlled by the same thermostat which controls the liquid nitrogen solenoid valve (e.g. valve 56 of FIG. 5). Thus, when nitrogen is flowing through the heat exchanger, a portion of the effluent nitrogen gas leaving the heat exchanger may be directed into the container together with air as shown in FIG. 9. CO builds up from the respiration of the fruit or vegetatble. The atmosphere may be controlled by using well known gas analyzers adapted to actuate solenoid valves when atmosphere control is called for. (Note block diagram of FIG. 13.)

As air brought into the truck to control the atmosphere is generally warm and, therefore, has a temperature diluting effect on the atmosphere in the trailer, I may use a heat exchange system for cooling the incoming air such as that shown diagrammatically in FIG. 10, the outline 115 representing a trailer, having ingress means 116 for outside air comprising a pathway 117 of metal running coaxially within and in heat exchange relationship with exit pathway 118 also of metal. The inlet air fiows along pathway 117 and into the trailer via flared opening 119 having a nozzle 120 coaxially located therein through which waste nitrogen gas from line 121 (from, for example outlet 28a of FIG. 2) flows to draw in with it air along pathway 117.

The atmosphere which is circulated within the trailer leaves the trailer by way of outer exit pathway 118 and cools the inlet air by heat exchange with the inner pathway 117. The amount of air drawn in can be determined by a pre-set valve as in FIG. 9 or in place of valves, small intake and outlet fans may be employed actuated by electrical components which in turn are actuated by sensing means associated with a gas analyzer.

A still further embodiment for controlling the amount of in-feeding of air from the atmosphere is shown in FIG. 11. A venturi 122 is shown entering the trailer through insulated wall 123, a nozzle 124 being located coaxially in the throat of the venturi, said nozzle being coextensive with nitrogen line 125 coming from the warm part of the heat exchanger in the trailer truck, such as shown at nitrogen exit 63 of FIG. 5. Across the mouth of the venturi is fixed an adjustable damper 126 for controlling the amount of air brought in by the aspirating effect of the flow at the nitrogen nozzle. The damper opening may be set at a predetermined opening or automatically actuated by sensing devices associated with a gas analyzer.

A system which may be employed to control the atmosphere in the refrigerated compartment is illustrated diagrammatically by FIG. 13. Atmosphere in the refrigerated compartment is passed through a gas analyzer 145 where the nitrogen/oxygen ratio is determined and optionally via valve 144 through carbon dioxide analyzer 145A. Sensing means are provided by the analyzers for actuating gas flow control means, e.g. solenoid operable valves 146 (nitrogen) or fans or other means, control means or valve 147 (air) and if desired, CO control means 148, said means being coupled across gas lines 149, 150 and 151, respectively. When the compartment calls for atmosphere make-up, at least nitrogen and air valves 146 and 147 are opened and possibly CO valve 148 if the CO happens to be low. The opening in valves 146 and 147 are set to provide the desired N /O ratio. Thus, gases from one or more of the lines 149, 150 and 151 flow to venturi 152, nitrogen line 149 extending into the throat of the venturi at 153 whereby to produce an aspirating effect in drawing in the other gases and cause mixing thereof before entering compartment 154 via line 155. The circulating atmosphere leaving the compartment passes through a solenoid controlled valve 156 (or this could be a fan) which in the embodiment shown may be actuated the same as solenoid valves 156 and 147 (or fans). Assuming a proportional amount of air and nitrogen is called for in the compartment, outlet valve 156 (or fan, if used) is caused to open together with the opening of gas flow control means 146 and 147. As nitrogen flows through the venturi, a proportioned amount of air is aspirated into the venturi depending upon the valve opening or where a fan is employed the amount of fan suction. When a balanced atmosphere is obtained as determined by the gas analyzer, the gas flow control means are closed.

As stated hereinbefore, carbon dioxide is generally produced as a result of respiration of the fruit or vegetable. However, should the gas analyzer call for more CO this can be added independently from the CO reservoir through gas flow control means 148.

FIG. 12 depicts another type of heat exchanger that can be employed to cool incoming air in controlling the atmosphere inside the trailer. The heat exchanger assembly comprises a heat exchanger casing of metal having an entry line 131 at one end carrying exit atmosphere from the truck and an exit line 132 at the opposite end through which the atmosphere is disposed of. Coaxially located within the casing is a set of heat exchange coils 133 having an air inlet end 134 extending outside the casing and on air exit end at which extends and is coupled to the back end of venturi 140. Within the casing, perforated bafiles 138 and 139 are provided across the openings of lines 131 and 132 to uniformly distribute the gas flowing through the casing in order to insure efii cient heat exchange with the incoming air passing through heat exchange coils 133.

The air line 135 and nitrogen gas line 137 enter venturi as shown where the proportioned amount of gases are mixed before they enter the truck.

My invention is advantageous in that it enables the reliable, convenient, and inexpensive use of liquid nitrogen. By using a heat transfer fluid to carry the cooling effect throughout the trailer or other food container, exceedingly uniform temperature is possible. By using this system, localized freezing and thawing is prevented. The system enables the cooling of the bottom of the trailer, as well as at the top and along the length of the trailer.

By using the preferred embodiment of employing a vaporizable heat transfer fluid hermetically sealed in an evacuated circulating system, any temperature variation in the system is easily corrected by the fact that the warmest portion of the heat transfer liquid will boil and remove the heat, regardless where the warm spot is or how close or far from the heat exchanger it is.

Because of the foregoing advantages, the contents of a truck can be packed as tightly as possible and no provision need be made for air circulation where that is not a problem. Originally, it was thought necessary by some to have to continue to keep food cold after it has been brought down to temperature. Actually, What is necessary is to remove any heat added at the place where it is absorbed. Since heat into the trailer is absorbed through the walls, I find by placing the tube panels around the food and next to the wall, any heat absorbed through the insulated Walls is removed by my system. Thus, it is not necessary to remove heat from the food since it will remain at the desired temperature.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be Within the purview and scope of the invention and the appended claims.

What is claimed is:

1. A refrigeration system for shipping perishable commodities comprising heat exchange means, means for maintaining said heat exchange means at a refrigerating temperature, a heat transfer circulating system configurated to surround substantially perishable commodities for controlling the temperature of said commodities, means coupling said heat exchange means in gravity-feeding circulation relationship to said heat transfer circulating system, said coupling means comprising a heat transfer fluid feed line and a heat transfer fluid return line, said heat transfer circulating system being evacuated, and a vaporizable heat transfer fluid hermetically sealed in said circulating system, the amount of said fluid in the liquid state being such that the major portion of the evacuated heat transfer circulating system is substantially flooded with said vaporizable fluid.

2. The refrigeration system of claim 1, wherein the means for mantaining the heat exchange means at a refrigerating temperature is a cryogenic vessel coupled thereto via a feed line, said vessel being adapted to con-fine therein a vaporizable cryogenic fluid maintained at a subzero temperature, said feed line having an automatically controllable valve therein for controlling the flow of cryogenic fluid to said exchange means.

3. The combination of a refrigeration system and an insulated transport compartment for shipping perishable commodities comprising means for refrigerating heat exchange means supported in said compartment, a heat transfer circulating system configurated to surround substantially perishable commodities to be protected, said circulating system being supported adjacent the Walls of said compartment surrounding said perishables, a heat transfer fluid feed line and a heat transfer fluid return line coupling said heat exchange means in gravity-feeding relationship to said circulating system, said heat transfer circulating system being evacuated, and a vaporizable heat transfer fluid in said heat transfer circulating system, the amount of said vaporizable fluid in the liquid being such that the major portion of the evacuated heat transfer system is substantially flooded with said vaporizable fluid.

4. The refrigeration system of claim 3, wherein the means for maintaining the heat exchange means at a refrigeration temperature is a cryogenic vessel coupled thereto via a feed line, said vessel being adapted to confine therein a vaporizable cryogenic fluid maintained at a subzero temperature, said feed line having an automatically controllable valve therein for controlling the flow of cryogenic fluid to said exchange means.

5. The combination of claim 3 including means for controlling the atmosphere surrounding the perishable commodities.

6. A refrigeration system for shipping perishable commodities comprising, a cryogenic vessel for confining liquid maintained at a sub-zero temperature, heat exchange means coupled to said vessel via a nitrogen feed line whereby to effect heat transfer between the contents of said vessel and said heat exchange means, a heat transfer circulating system configurated to surround perishable commodities to be protected, a heat transfer fluid feed line and a heat transfer fluid return line coupling said heat exchange :means to said circulating system, a heat transfer fluid in said heat transfer circulating system, the amount of said fluid in the liquid state and the relative position of the heat exchange means to the circulating system being such that the major portion of the heat transfer circulating system is substantially flooded with said heat transfer fluid, means for controlling the atmosphere surrounding the perishable commodities comprising, means for feeding nitrogen gas from the heat exchanger into the atmosphere surrounding said perishable commodities, means associated with said nitrogen gas feeding means for mixing proportioned amounts of air with said nitrogen and feeding said mixture into said atmosphere surrounding said perishables, and means for continuously replacing said atmosphere with said mixture.

7. The refrigeration system of claim 6, wherein the heat transfer circulating system is evacuated, wherein the heat transfer fiuid is a vaporizable fluid hermetically sealed therein, wherein said heat transfer fluid line coupling said heat, exchange means to said circulating system is a liquid feed line, and wherein said fluid return line coupling said circulating system to said heat exchange means is a vapor return line.

8. The refrigeration system of claim 6, wherein the nitrogen feed line connected to said heat exchange means has coupled thereto a solenoid operable valve, wherein a temperature sensing means is provided for sensing temperature changes of perishable commodities to be protected and wherein a powered actuating circuit is provided coupling said solenoid operable valve to said temperature sensing means, whereby when a temperature rise is sensed, said solenoid operable valve is actuated to release liquid nitrogen to the heat exchange means to supplement the cooling effect of said heat transfer fluid.

9. A refrigeration system for shipping perishable commodities comprising a cryogenic vessel for confining liquid nitrogen maintained at a sub-zero temperature, heat exchange means comprising a cyclone coupled to said vessel via a nitrogen feed line whereby to effect heat transfer between the contents of said vessel and said cyclone, a heat transfer circulating system configurated to surround perishable commodities to be protected, a heat transfer fluid feed line and a heat transfer fluid return line coupling said cyclone in circulation relationship with said heat transfer circulating system, a heat transfer antifreeze liquid in said circulating system, the amount of said liquid and the relative position of the heat exchange :means to the circulating system being such that the major portion of the heat transfer circulating system is substantially flooded with said heat transfer liquid, a pump coupled to the heat transfer fluid return line for pumping the antifreeze liquid to said cyclone, said nitrogen feed line being coupled to said cyclone coaxially with the heat transfer liquid return line whereby to mix with the anti-freeze liquid entering said cyclone, said cyclone having exit means open to the atmosphere for allowing gaseous nitrogen to leave the cyclone after separation from the antifreeze liquid.

10. The combination of a refrigeration system and an insulated transport compartment for shipping perishable commodities, a cryogenic vessel in said compartment for confining a liquid nitrogen therein at a sub-zero temperature, heat exchange means supported in said compartment coupled to said vessel via a nitrogen feed line whereby to effect heat transfer between the contents of said vessel and said heat exchange means, a heat transfer circulating system configuratcd to surround substantially perishable commodities to be protected, said circulating system be ing supported adjacent the walls of said compartments surrounding said perishables, a heat transfer fluid feed line and a heat transfer fluid return line coupling said heat exchange means to said circulating system, a heat transfer fluid in said heat transfer circulating system, the amount of said fluid in the liquid state and the relative position of the heat exchange means to the circulating system being such that the major portion of the heat transfer circulating system is substantially flooded with said heat transfer fluid, means for controlling the atmosphere surrounding the perishable commodities, comprising means for feeding nitrogen gas from the heat exchanger into the atmosphere surrounding said perishable commodities, means associated with said nitrogen gas feeding means for mixing proportioned amounts of air with said nitrogen and feeding said mixture into said atmosphere surrounding said perishables, and means for continuously replacing said atmosphere with said mixture.

11. The combination refrigeration system and transport compartment of claim 10, wherein the heat transfer circulating system is evacuated, wherein the heat transfer fluid is a vaporizable fluid hermetically sealed therein, wherein said heat transfer fluid line coupling said heat exchange means to said circulating system is a liquid fluid line, and wherein said fluid return line coupling said circulating system to said heat exchange means is a vapor return line.

12. The combination refrigeration system and transport compartment of claim 10, wherein the nitrogen feed line connected to said heat exchange means has coupled thereto a solenoid operable valve, wherein a temperature sensing means is provided for sensing temperature changes of perishable commodities to be protected and wherein a powered actuating circuit is provided coupling said solenoid operable valve to said temperature sensing means, whereby when a temperature rise is sensed, said solenoid operable valve is actuated to release liquid nitrogen to the heat exchange means to supplement the cooling effect of said heat transfer fluid.

13. The combination refrigeration system and transport compartment of claim 10, wherein said heat exchange means is a cyclone coupled to said circulating means, wherein said heat transfer fluid in said circulating system is an anti-freeze liquid, wherein said liquid return line of the heat transfer fluid is coupled to said cyclone and has a pump coupled therein to pump said liquid to said cyclone, wherein said liquid nitrogen line is coupled to said cyclone coaxially with said liquid return line whereby to mix with the anti-freeze liquid entering said cyclone, and wherein said cyclone has exit means open to the atmosphere for allowing gaseous nitrogen to leave the cyclone after separation from the anti-freeze liquid.

14. The combination of a refrigeration system and an insulated transport compartment for shipping perishable commodities comprising, means in said compartment for confining liquid nitrogen maintained at a sub-zero temperature, heat exchange means supported in said compartment cooperably associated with said nitrogen confining means whereby to effect heat transfer between the contents of said confining means and said heat exchange means, a heat transfer circulating system configuratcd to surround substantially perishable commodities to be protected, said circulating system being supported adjacent the walls of said compartment surrounding said perishables, a heat transfer fluid feed line and a heat transfer fluid return line coupling said heat exchange means to said circulating system, and a heat transfer fluid in said heat transfer circulating system, the amount of said fluid in the liquid state and the relative position of the heat exchange means to the circulating system being such that the major portion of the heat transfer circulating system is substantially flooded with said heat transfer fluid, means for controlling the atmosphere in said transport compartment comprising means for analyzing said atmosphere, and gas flow control means for feeding oxygen and nitrogen into said compartment in accordance with the atmosphere requirements.

15. The combination refrigeration system and transport compartment of claim 14 including gas control flow means for adding make-up carbon dioxide to said compartrnent.

References Cited UNITED STATES PATENTS 2,931,192 4/1960 Weinberg 62434 X 3,241,329 3/1966 Fritch, et al. 62239 3,247,678 4/1966 Mohlman 62199 3,255,597 6/1966 Carter 62--239 3,287,925 11/1966 Kane et al. 62-5l4 3,304,739 2/1967 Erath 62-45 X 3,308,630 3/1967 Fritch et al. 62-52 3,316,726 5/1967 Pauliukonis 6255 3,225,558 12/1965 Wulfken 62-167 LLOYD L. KING, Primary Examiner; 

